New England Patriots coach Bill Belichick today said "climatic conditions" may have been to blame for the footballs that were under-inflated Sunday for the AFC Championship game, and said the team had not tried to tamper with them.

He said the team "followed the rules to the letter," denying any intentional wrongdoing by the Patriots.

"At no time was there any intent whatsoever to try to compromise the integrity of the game or to gain an advantage," Belichick said.

The NFL acknowledged for the first time Friday that the Patriots used under-inflated balls in the first half of Sunday's game against the Indianapolis Colts, a game the Patriots won 45-7 to advance to the Super Bowl.

"While the evidence thus far supports the conclusion that footballs that were under-inflated were used by the Patriots in the first half, the footballs were properly inflated for the second half and confirmed at the conclusion of the game to have remained properly inflated," the league said in a statement.

"The goals of the investigation will be to determine the explanation for why footballs used in the game were not in compliance with the playing rules and specifically whether any noncompliance was the result of deliberate action. We have not made any judgments on these points and will not do so until we have concluded our investigation and considered all of the relevant evidence," the league said, adding that it has conducted nearly 40 interviews, including "Patriots personnel, game officials, and third parties with relevant information and expertise."

The NFL also said it is continuing to look the matter ahead of next week's Super Bowl.

In a statement Friday, Patriots owner Bob Kraft said, "Immediately after receiving the letter [from the NFL on Monday], I instructed our staff to be completely cooperative and transparent with the league's investigators. During the three days they were here, we provided access to every full- and part-time employee the league's representatives requested to speak with and produced every communication device that they requested to search. It is an ongoing process that the league and our team are taking very seriously. ... Competitive balance and the integrity of the game are the foundation of what makes our league so special and I have the utmost respect for those principles. Our organization will continue to cooperate throughout the league's investigation. Meanwhile, our players, coaches and staff will continue to focus on our preparations for Super Bowl XLIX and the many challenges we face as we prepare for the Seattle Seahawks."

Earlier this week, Belichick and Patriots quarterback Tom Brady denied knowing that the footballs used at Gillette Stadium in Foxborough, Massachusetts, were deflated.

Belichick said today the Patriots "welcome" the NFL's investigation of the incident.

The NFL's guidelines dictate that a ball must be inflated to about 12.5 and 13.5 pounds per square inch and weigh between 14 and 15 ounces.

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